Electrical System for a Computer Cart

ABSTRACT

An electrical system for a computer cart enables power to be diverted between electrical channels within the cart using an intelligent round robin charging scheme. All power may be diverted to individual channels one at a time for short charging intervals. When a selected primary channel does not require all available power within the cart, excess power is provided to a secondary channel. All three channels may likewise share power if excess is available. Relays are used to allow power to be controlled to the individual channels. Current sensors on each channel sense an amount of current used by the channel. The output of the current sensor is digitized and integrated to determine how much current is being used by the channel. The current is used by the control to detect uncharged laptops and to selectively divert power between channels to optimize use of power within the computer cart.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of international applicationPCT/US2010/021270, filed Jan. 15, 2010, which claims priority to U.S.Provisional Patent Application No. 61/145,685, filed Jan. 19, 2009,entitled COMPUTER CART, the content of each of which is herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to computer storage systems and, moreparticularly, to an electrical system for a computer cart.

2. Description of the Related Art

Computers, such as laptop computers and tablet computers, are commonlyused in educational facilities. When not in use, the computers aregenerally required to be stored in a secure manner to prevent them frombeing stolen or tampered with. Accordingly, it is common to store thecomputers in a lockable cart that will deter the students and otherpeople from accessing the computers without permission. Often the cartis provided with wheels so that it may be moved to different places sothat the computers may be used in different classrooms.

Conventional laptop computers include a battery that may be charged toenable the laptop to be used while not connected to an electricaloutlet. When the laptop is to be charged, an electrical adapter is usedto convert 120/240 volt 60/50 Hz AC electrical power available in astandard electrical outlet to a lower voltage DC form. For example, theelectrical adapter may convert available line power to 19.5 volt or 24volt DC power which is then input to the computer to charge the battery.

Electrical adapters may come in different sizes, but often the adapterwill be on the order of 6 inches long, 2-3 inches wide, and 1-2 inchesthick. Colloquially, electrical adapters are often referred to as“bricks” although other terms may also be used to refer to these typesof electrical adapters.

Each electrical adapter typically includes two cords—one cord thatenables the electrical adapter to be plugged into an electrical walloutlet, and another cord that enables the electrical adapter to beconnected to the computer. Since the electrical adapter is used when thecomputer is charging as well as when the computer is plugged in duringoperation, the cords are frequently relatively long. For example, thecord that plugs into the wall outlet may be 3-4 feet long and the othercord that connects the computer to the adapter may be 5-6 feet long.These lengths are merely examples, as other length cords may be used aswell. Depending on the implementation, however, the overall cord lengthmay be on the order of 10 feet.

Many computer carts are designed to enable laptop computers to becharged while stored within the computer cart. Accordingly, it would beadvantageous to provide an intelligent way to distribute power within acomputer cart.

SUMMARY OF THE INVENTION

The following Summary and the Abstract set forth at the end of thisapplication are provided herein to introduce some concepts discussed inthe Detailed Description below. The Summary and Abstract sections arenot comprehensive and are not intended to delineate the scope ofprotectable subject matter which is set forth by the claims presentedbelow.

An electrical system for a computer cart enables power to be divertedbetween electrical channels within the cart using an intelligent roundrobin charging scheme. All power may be diverted to individual channelsone at a time for short charging intervals. When a selected primarychannel does not require all available power within the cart, excesspower is provided to a secondary channel. All three channels maylikewise share power if excess is available. Relays are used to allowpower to be controlled to the individual channels. Current sensors oneach channel sense an amount of current used by the channel. The outputof the current sensor is digitized and integrated to determine how muchcurrent is being used by the channel. The current is used by the controlto detect uncharged laptops and to selectively divert power betweenchannels to optimize use of power within the computer cart.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present invention are illustrated by way of example inthe following drawings in which like references indicate similarelements. The following drawings disclose various embodiments of thepresent invention for purposes of illustration only and are not intendedto limit the scope of the invention. For purposes of clarity, not everycomponent may be labeled in every figure. In the figures:

FIG. 1 is a front perspective view of a computer cart according to anembodiment of the invention;

FIG. 2 is a rear perspective view of the computer cart of FIG. 1;

FIG. 3-7 are perspective views of an embodiment of the computer cart ofFIG. 1 showing successive stages of construction of the computer cart;

FIGS. 8-15 are perspective views of another embodiment of the computercart of FIG. 1 showing successive stages of construction of the computercart;

FIGS. 16-17 are perspective views of door assemblies that may be used onthe computer cart of FIG. 1; and

FIGS. 18-21 show an electrical system for use in the computer cart ofFIG. 1.

DETAILED DESCRIPTION

FIGS. 1-17 illustrate two embodiments of a computer cart 10 for designedto maintain a large number of portable computers such as laptop ortablet computers. The computer cart 10, as described in greater detailbelow, has segregated computer storage areas and adapter/cord managementareas. This enables the adapters and cords to be stored in an orderlyfashion and also prevents the cords and adapters from being accessed orremoved when the computers are being removed from the cart or replacedinto the cart.

FIGS. 1-17 show two separate embodiments of the invention. Specifically,FIGS. 3-8 show an embodiment that is designed to store laptop computershorizontally, whereas FIGS. 9-17 show an embodiment that is designed tostore laptops vertically. The exterior appearance of the two embodimentsis similar, however, and FIGS. 1-2 show the overall exterior appearanceof both embodiments of the laptop cart. Likewise, FIGS. 16-17 show anexample door structure and FIGS. 18-21 show example electrical systemsthat may be used with either embodiment of the computer cart. Since thetwo embodiments store computers in different orientations, the interiorspace of the two embodiments has been adjusted to accommodate differentstorage requirements.

As shown in FIG. 1, the computer cart 10 is generally is formed as acabinet mounted on wheels 12 that are configured to enable the cart tobe mobile. The wheels may be castors or other types of wheels. Thecomputer cart 10 is designed to store laptop computers and to charge thelaptop computers while stored therein. Charging laptop computersgenerates heat, which is required to be dissipated from the cart so asto not overheat the computers. Accordingly, ventilation holes 14 areincluded in the outer surfaces of the computer cart to enable air tocirculate into and out of computer cart 10. The ventilation holes may belocated as shown or may be formed in another decorative pattern ifdesired. The particular number of ventilation holes will depend on thenumber of laptops the cart is designed to contain as well as theanticipated heat output of the laptops. The ventilation apertures may beshaped as rectangles with rounded ends as shown or may be formed usingother shapes. The ventilation apertures enable air to circulate betweenthe interior and exterior the computer cart to enable heat generated bythe computers within the computer cart to be dissipated.

FIG. 3 is a lower perspective view of the computer cart showing theinterior structure of the frame of the computer cart and showing how thewheels 12 are attached to the laptop cart. As shown in FIG. 3, thecomputer cart 10 generally includes frame 16 designed to give structuralrigidity to the computer cart and to generally define the overall shapeof the cart. Side panels 18 are attached to the frame, for example bywelding, rivets, or using removable fasteners. The side panels in theillustrated embodiment are not movable relative to the frame onceinstalled and are designed to enclose the computer cart without enablingusers to access the computers through the sides of the computer cart.The computer cart also includes bottom panel 20 which, like side panels18, may be attached to the frame by welding, rivets, or using removablefasteners. The panels are preferably formed from steel or other suitablysolid material to deter thieves from attempting to cut through thematerial forming panels 18, 20, to access computers stored within thecomputer cart 10.

FIG. 3 also shows how wheels 12 and bumpers 22 are installed on computercart 10. As shown in FIG. 3, wheels 12, which may be implemented usingcastors, are connected to the cart 10 using screws 24. Alternativelyother mechanical fasteners may be used. The screws 24 affix wheels 12 toextension plates 26 mounted to the frame 16 or forming part of frame 16.The extension plates 26 extend a short distance out from the frame 11 oneach of the corners of the computer cart. Protective bumpers 22 areattached to the ends of the extension plates 26 to soften the ends ofthe extension plates 26 and provide a cushion for the computer cart at alocation where the cart is most likely to come into contact withexternal objects.

Where the wheels are implemented using castors, the castors may bedirectional locking castors as well as motion locking castors. Castorsof this nature typically have two levers—one that locks the direction ofthe castor and the other that locks the wheel from moving. To move thecomputer cart under normal conditions, two of the castors may be lockedto be directionally aligned with the computer cart while the other twocastors swivel. However, for maneuvering the cart in tight quarters, theother two castors may be directionally unlocked so that all four castorscan swivel. Once the cart is positioned, the other lever may be used tolock the wheels to prevent the wheels from moving and, hence, preventthe cart from rolling so that the cart will remain in a fixed position.Other types of castors may be utilized as well.

As shown in FIG. 4, the computer cart 10 includes a dividing panel whichis inserted into the computer cart between side panels 18 and whichdivides the computer cart into a front compartment 30 and rearcompartment 32. The dividing panel 18 extends generally parallel to thefront of the cart, and also generally parallel to the rear of the cart,so that the front and rear compartments have approximately constantdepth across the width of the cart. As is visible from FIG. 5, thedividing panel is located within the interior of the cart toward theback of the cart so that the rear compartment 32 of the cart 10 isshallower (does not extend as far into the cart) than the frontcompartment 30. In operation, as described below, the front compartmentof the cart will be used to store the laptop computers while the rearcompartment of the cart will be used to store the AC adapters and powercords.

The dividing panel 28 may be provided with slots 34 (see FIG. 4)thatmate with tabs 36 within cart 10 to enable the dividing panel to besecured within the computer cart. Screws or other mechanical fastenersmay be used to fasten the dividing panel within the computer cart.Alternatively, the dividing panel may be welded or other mechanicalfasteners may be used to secure the dividing panel within the cart.

As shown in FIG. 4, apertures 38 are included within dividing panel 28both for ventilation and to enable power cords from the AC adapters tobe fed through the dividing panel from the rear of the cart to the frontof the cart. Optionally a rubber gasket may be used to hold the wire inplace within the aperture to prevent it from being pulled forward intothe front compartment of the cart. Alternatively, a thin gasket,grommet, or washer may be inserted on the edges of the aperture toprevent the wire from rubbing against any potentially sharp edges of theaperture that may have been formed during manufacturing.

In the embodiment shown in FIGS. 4-5, the dividing panel 28 includes aplurality of elongated horizontal slots 40 designed to receiveextensions 42 of shelves 44. The extensions 42 of shelves 40 fit throughthe horizontal slots 40 in dividing panel 28 to create small shelves 46within the rear compartment of the cart 10. The small shelves 46 arebest shown in FIG. 7. The shelves 44 may be connected to the side panels18 and the divider panel 28 using screws or other mechanical fasteners.

Each of the small shelves 46 is sized to hold a standard sized ACadapter and includes integrated cord management indentations 48. Sincecurrent AC adapters are approximately 6 inches long, the shelves may beon the order of 6 inches long as well. Other dimensions may be utilizedas well depending on the particular implementation. Power strips 50 areincluded along the edges of the rear compartment of the cart (see FIG.7) to provide power receptacles in the vicinity of the small shelves 46.

In operation, an AC adapter for each of the computers to be stored inthe computer cart will be placed on its own small shelf 46. The ACadapters will be plugged into outlets 52 contained in the power strip 50and any excess power cord not required to span the distance from theshelf where the AC adapter is stored and the selected outlet 52 will bewrapped around the AC adapter and shelf 46. The cord managementindentations 48 in the small shelf will help hold the cords in placewhile wrapped around the AC adapter and shelf to provide integrated cordmanagement for each computer stored in the computer cart.

The low voltage cords that are used to connect the AC adapters to thecomputers will be fed through selected apertures in the divider panel toenter the front compartment above a shelf where the associated computeris to be stored. A washer or other soft structure may be provided withinthe aperture to protect the cords from any sharp edges associated withthe aperture. Alternatively, the apertures may be splayed to provide asmooth surface at the point of contact between the cord and the dividerpanel. A sufficient length of cord should be fed into the interiorcompartment to enable a user to conveniently plug the end of the cordinto a laptop computer to be inserted into the cart. The low voltagecord will thus extend over the top of shelf 44 to enable the cord to beinserted into a power receptacle on the computer so that the computermay be charged while being stored on the shelf. Any excess low powercord not required to be available within the front compartment may bewrapped around the AC adapter and small shelf and held in place withinthe rear compartment of the cart via cord management indentations.

In FIGS. 5-8, the shelves have been shown as not including ventilationapertures which helps to prevent heat from being vertically transmittedfrom the lower laptops to the upper laptops. If desired additionalapertures may be included within these shelves to further facilitatepassive ventilation. The shelves do not extend all the way to the sidepanels, however, so that a chimney of air may flow within the cart alongthe side panels. Active ventilation, e.g. one or more fans, may also beincluded if necessary to achieve adequate heat dissipation from thefront and/or rear compartments of the cart.

The number of shelves and width of the shelves contained within thecomputer cart determines the carrying capacity of the computer cart. Inthe illustrated example, the computer cart includes six shelves, each ofwhich can hold up to three laptops. In another embodiment, the width ofthe shelves may be adjusted to accommodate fewer or additionalcomputers. In the illustrated embodiment, the computer cart is designedto carry and charge 20 laptops total (3 on each shelf and 2 on thebottom panel 20). These 20 laptops plug into 20 outlets 52 on powerstrips 50 (10 outlets per power strip) to enable all of the laptops tocharge without plugging/unplugging sets of laptops. Other non-chargingequipment may be stored in the laptop cart as well if desired. Additionof extra shelves or lengthening of the shelves may enable the laptopcart to hold larger numbers of laptops. In this instance, the number ofpower strips 50 or the number of outlets per power strip may beincreased to accommodate the larger number of laptops.

The shelves are spaced vertically to enable the computers to be storedin the computer cart while partially open—i.e. without requiring the LCDdisplay to be shut into the base of the computer. This enables thecomputers to remain active/alive while stored in the computer cart sothat the computers may be updated/synchronized while stored in the cart.

The computer cart 10 has a pair of front doors 54 on the front and asecond pair of rear doors 56 on the back. Preferably, the doors arerecessed into the frame of the cart to make it more difficult to pry thedoors open when locked. The front doors 54 provide access to the frontcompartment of the cart 30 and the rear doors 56 provide independentaccess to the rear compartment of the cart 32. By having separate accessto the rear compartment of the cart, the AC adapters and wire managementmay be independently secured, so that students or other individualsauthorized to use the computers cannot access the AC adapters and excesswiring. This makes the computer cart appear neater from the front andalso provides a security measure to ensure that the AC adapters or oneor more wires does not accidentally go missing. In one embodiment, bothsets of doors may be folded to be flat along the sides of the computercart.

The front doors 54 and rear doors 56 are each provided with a handle 60.Additional details about the handle are shown in FIGS. 16 and 17. Asshown in FIG. 16, one side of the door includes a locking mechanism 62including two rods 64 that are designed to extend through brackets 66and engage into apertures 68 in a frame 16 of the computer cart. Whenthe rods enter the apertures 68, the rods secure the door to the frameso that the doors are not able to be opened except upon application ofexcessive force.

The handle 60 includes a lever 70 having a square shaft 72. The squareshaft 72 mates with a square aperture 74 in plate 76. The plate 76 hastwo radially opposite apertures 78 that enable the rods 64 to berotatably attached to the plate 76. A rivet or other mechanical fastenermay be used to attach the rods to the plate 76. In operation, a personmoves the lever 70 which causes the square shaft 72 to rotate. Thiscauses the plate 74 to rotate, so that the holes are either verticallyaligned (in which case the rods are pushed up/down into apertures 68) orthe holes are horizontally aligned (in which case the rods are pulledout of the apertures 68). In this manner the lever enables the doors tobe locked.

In the embodiment shown in FIGS. 16-17, one door has a locking mechanismand the other door does not have a locking mechanism (FIG. 17). The doorwithout the locking mechanism may have a lip 80 formed on the insideedge (where it will abut the other door) so that the door with thelocking mechanism can hold the other door closed. Optionally, amatching, albeit fixed, lever 82 may be provided on the door without alocking mechanism. If desired, a pair of apertures 84 may be provided inmovable lever 70 and fixed lever 82 to enable the doors to be securedwith a padlock 86 (see FIG. 1).

The cart is equipped with a handle 90 (see FIG. 1) on either side thatwill enable the cart to be grasped to be moved by an operator. As shownin FIG. 1, the handle 90 may be formed from a flattened tubular bar thatis connected to the cart by brackets 92. Optionally, end caps 94 may beprovided to enclose the interior of the tubular bar. Other handle shapesmay be used as well.

Preferably the brackets 92 may be disposed inward from the end of thehandle a short distance, i.e. an inch or two, to enable the handle to beused for power cord management. Specifically, the computer cart isequipped with a power cord that will enable the computer cart to beplugged into an ordinary wall outlet. The power cord may be storedwithin the rear compartment or, alternatively, passed through anaperture in the computer cart to be accessible outside of the rearcompartment. When the cord is not plugged into the wall outlet, the cordmay be wrapped about the brackets 92 holding the handle to the cart sothat the cord can be wound for storage during transit without requiringthe cord to be tucked away into the rear compartment. Alternatively, aseparate set of power cord management brackets may be attached to theside of the computer cart or to one of the rear doors of the computercart to enable the cord for the computer cart to be secured when not inuse.

FIGS. 8-15 show another embodiment in which the laptop cart 110 isdesigned to store laptops vertically. This embodiment is similar to theprevious embodiment (FIGS. 3-7) in that the cart is formed as a cabinethaving a dividing panel 128 separating the interior of the cart into twocompartments—a front compartment 130 and a rear compartment 132. As inthe previous embodiment, the dividing panel has a plurality of apertures138 for ventilation and to enable low voltage power cables from the ACadapters to be passed from the front compartment where the laptops arestored to the rear compartment where the AC adapters are stored.

As shown in FIGS. 12-13, since the laptops are stored vertically on edgewithin the cart, the vertical spacing between the shelves is increasedto enable the laptops to be stored while standing on edge. Thus, in theillustrated embodiment, only one shelf 144 is included within the frontcompartment of the cabinet, which may be anchored to the frame of thecabinet using tabs/slots and appropriate mechanical fasteners. The shelf144 is also attached to the dividing panel to provide support along thelength of the shelf. If larger numbers of laptops are to be storedwithin the computer cart, the shelf may be extended or the height of thecart may be increased to accommodate extra shelves.

Unlike the previous embodiment, the shelf does not extend through thedivider panel. Rather, the shelf terminates at the divider panel(although tabs from the shelf may extend through slots in the dividerpanel to help secure the shelf along the divider panel. A wire bracket170 may be used to hold laptops in place within the front compartment.

Wire management, and AC adapter storage, is provided in this embodimentthrough the use of trays 200 (see FIG. 14). Trays 200 have tabs 202 thatextend through slots 204 in the dividing panel 128 and are then screwedin place. Additional screws may be used to secure the trays on thedividing panel as well. Note, in this embodiment, that the dividingpanel does not have any apertures in a region 206 that will be used toreceive tray 202. Rather all the ventilation holes and wire managementholes in the dividing panel are disposed either above the trays 202,below the trays 202, or in-between the trays 202. Alternatively,individual vertical shelves may be used to hold the AC adapters for eachof the computers to be stored within the computer cart.

Three power strips 150, each having 10 outlets 152, are disposed aboutthe perimeter of the rear compartment of the computer cart. In theillustrated embodiment, one power strip is disposed on the left edge,one on the right edge, and one along the top edge. The power strips arearranged to provide easy access to the power for AC adapters storedwithin the trays.

In operation, an AC adapter for each laptop computer to be stored withinthe laptop cart will be plugged into one of the outlets 152 and theexcess power cord will be wrapped around the AC adapter. Likewise thelow voltage cord will be fed through one of the apertures into the frontcompartment of the laptop cart via one of the apertures immediatelyabove the tray. The low voltage cords should be spaced out along thetray to go through apertures at locations where the laptops will bestored within the front compartment. For example, if the laptops arestored every 2.5 inches within the front compartment, then the lowvoltage power cords should likewise be passed through apertures from therear compartment to the front compartment approximately every 2.5 inchesalong the divider panel.

The cart has a power module that allows power to be distributed withinthe cart to charge the laptops stored in the computer cart. An exampleof how the power module may be formed is shown in FIGS. 1-2. As shown inFIGS. 1-2, in this embodiment, the power module 190 of the computer cart10 includes two auxiliary outlets 191, an on-off switch 192, a pluralityof LEDs 193, 194, and a mode selection button 195. An additionalaccessory outlet may also be provided inside the rear compartment of thecomputer cart to enable a peripheral, such as a wireless router, to beplugged into the computer cart. The power switch 192 may be implementedas a light-up toggle switch and enable the computer cart to be turnedon/off while plugged into a wall outlet. The mode selection button 195is used to control which electrical features of the cart are activewhile the computer cart is turned on.

The power module in the illustrated embodiment has two banks of fiveLight Emitting Diodes (LEDs) 193, 194 that provide status indications tothe operator. In another embodiment, the power module has fewer LEDssuch as three LEDs and, accordingly, different numbers of LEDs may beused. In the illustrated embodiment, the power module has a first bankof LEDs 193 on a top surface and a second bank of LEDs on a frontsurface. Having the LEDs on the top surface enables a person standing bythe computer cart to see how the cart is operating. Having the LEDs onthe front surface of the power module enables the operator to see howthe cart is operating when the operator is further away from the cart,such as if the operator is across the room. This allows a person runningthe computer cart to monitor the status of the cart and of the computerscharging within the cart from a distance.

The computer cart may use different LED color combinations to indicatethe status of the computer cart (i.e. which outlets are active) and toindicate the charge status of the computers stored within the art. Inone embodiment, the computer cart includes five LEDs in each bank: oneyellow LED, three blue LEDs, and one amber LED. When the power switch isturned on, the switch 192 is illuminated indicating that power is now oninside the cart. This also indicates that the hidden accessory and topaccessory outlets 191 are on; the accessory outlet will be on wheneverthe cart is turned on. The other LEDs indicate which of the banks ofcomputers within the cart are charging and the charge status of thecomputers within the computer cart.

A normal wall outlet generally provides 15 amps of current. Since thisis not sufficient to simultaneously charge 30 laptops when the laptopsare fully discharged, the power module enables the operator to selecthow the laptops should be charged. In one embodiment, the operator mayelect to charge all laptops in a intelligent round robin manner, inwhich each bank of computers will be set as the priority channel and becharged for a relatively short, e.g. 3 minute interval, before the nextbank of computers is charged for a similar interval as next prioritychannel (The next priority channel of the last one is the first one).During this process, the priority channel for sure will get the powerfor the whole duration. If there is still power budget left over, thenon-priority channels will also get power. When there is enough powerfor all the 30 laptops to be charged simultaneously, such as where thelaptops are partially charged and thus need less power, the power willget distributed to all of the channels to minimize the total chargingtime.

The operator may also use the mode button to select to have one selectedbank of computers charged continuously for a period of time so that allpower is directed to that one bank of computers rather than being sharedin a round-robin fashion between all three banks Selection betweencharging modes may be made via mode selection button 195 or in anothermanner.

The lights on the power module enable the operator to know which laptopsare charging. In one embodiment, if the operator selects the round robincharging mode, the yellow LED will come on to indicate that all laptopsare charging. The three blue LEDs will flash as round robin power movesfrom power strip to power strip. When the system detects that alllaptops connected to a particular strip are charged, the system willindicate the charged status via the LEDs. If the computer cart is in theintelligent round robin mode of charging, power will be diverted awayfrom the channel connected to the charged laptops to make the poweravailable to the other channels if necessary.

The power module also has the ability to provide all power to one of thepower strips rather than sending power to all computers in a round robinmanner. In this “turbo” charging mode, the one of the blue LEDs will beilluminated to indicate which power strip, and hence which bank ofcomputers, is being charged.

Power may also be directed to the auxiliary outlets. Some auxiliarydevices, such as printers and projectors, may consume a relatively largeamount of power. In one embodiment, the operator may elect to have allpower directed to the auxiliary outlets. When the user elects this mode,the amber light is used to indicate that all power in the cart has beendiverted to the auxiliary outlets on the power module.

The operator of the cart may control which mode is used to charge thelaptops. For example, a mode selection button 195 may be provided on thepower module. When the operator presses the button one time, the yellowLED may be illuminated to indicate that the user has entered a mode inwhich all computers in the cart are to be charged in a round-robinmanner. If the user presses the button a second time, turbo mode for oneof the three banks of computers (one of the power strips) may beentered. Successively pressing the button an additional time will selecta subsequent bank of computers. Depending on the number of banks ofcomputers, the user may have to press the mode selection button two,three, or more times to cycle through each bank of computers. Finally,pressing the button an additional time will enter the operational modewhere all of the power is diverted to the auxiliary outlets.

Second generation carts increased the capacity of the charging cart toas many as 30 notebooks or laptops. Charging such a large number ofnotebooks simultaneously exceeds the current capacity of a single ACcircuit. Accordingly, previous carts had time-shared the output ofsingle AC wall outlet by using electromechanical timers to solve theover-current problem. The cart's internal AC power distribution wouldprovided to a power strip for a relatively long period of time, e.g. for2 hours, to charge the computers connected to that power strip. Then,power would be diverted to another power strip for two hours, andfinally diverted to the third power strip for two hours. In this manner,all 30 laptops within a cart could be charged within around 6 hours.

While this type of timing functioned well, it was found that if thelaptops were still warm from use when they were plugged into the cart,that some of the computers would be exposed to an additional two hoursof thermal stress if they were plugged into an active strip, while othercomputers would be allowed to cool for two or four hours beforecharging. This resulted in uneven stress on the set of computers storedin the cart. Likewise, a notebook with a battery deeply discharged mayhave to wait as long as four hours before a charging cycle would save itfrom permanent damage. And finally, a short-cycle condition could existwhere after three hours in the cart, some laptops would be fullycharged, others partially charged and still some experiencing nocharging at all.

According to an embodiment, a control circuit is used to greatlydecrease heat and electrical stress on the computers rendering fastertime to recharge while helping to maintain battery health. By chargingthe batteries for shorter intervals, each computer is provided with amore equal opportunity to be charged once placed in the cart. Thisallows more even treatment of the set of laptops to avoid excessivethermal stress to particular laptops and to quickly provide charge toany deeply discharged batteries to avoid storing the batteries in thedeeply discharged state for prolonged periods.

In one embodiment, an “Intelligent Round-Robin” charging scheme is usedwhich switches power between outlet strips every three minutes (or othershort interval) giving priority to the power strips that require themost amount of power first. Every strip also gets at least a 3 minute“relaxation cycle” once every six minutes to cool down after extendeduse or between charge cycles. By doing this, the computer cart can avoidany long delay time to start charging batteries in deep discharge—nomore than 6 minutes will elapse before a battery begins charging,regardless of which power strip the computer is connected to.

The intelligent round-robin charging scheme also enables short-cyclerecharge ability to be implemented for hungry laptops while charge allthe laptop at the shortest possible time. Specifically, since each powerstrip will get at least 3 minutes of charging every 9 minutes, after anhour all units present in the computer cart during that charging periodwill have at least a useful partial charge. Further, thermal levelingthrough the 3 minute basic cycle using the Intelligent Round Robinfeature ensures that no single bank of laptops are left on for aprotracted period without a cool down cycle. This reduces the amount ofheat generated by the laptops as a whole, which enables the computercart to charge a large number of computers while using passive coolingrather than requiring active cooling, e.g. via noisy fans. When all thecomputer get charged to certain extend thus draw less current andgenerate less heat, the system switch more channels to be charged alltogether to short the total charging time dramatically.

In one embodiment, the control 210 receives input from current sensorson each of the channels to determine the amount of current beingconsumed on that channel. The control receives an analog signal(waveform) representing the amount of current being drawn by the channeland samples the waveform multiple times during a given cycle. Forexample, the control may sample the current 80 times during a given ACcycle or during a given half AC cycle. The control 210 will integratethe sampled cycle to determine how much current was used during thecycle to thereby determine the amount of current being drawn by thechannel. The control will do this independently for each channel.

Knowing how much current is being drawn from each channel enables thecontrol to more intelligently distribute power within the laptop cart.When the laptop cart is loaded with laptops having depleated batteries,each channel is likely to require a considerable amount of power. Hence,the control 210 will cause all available power to be switched to one ofthe channels. The controller will provide power to that channel forthree minutes and then divert all power to another channel. Thecontroller will switch channels each three minutes to provide each ofthe channels with power for a period of time.

As the laptops start to charge, the laptops will draw less current.Hence, after a while, the control will determine that the channel is notusing all of the power within the cart. Hence, it will switch some ofthe excess power to a second channel. The control will continue to havea primary channel which receives all of the power it is able to consume.The excess power will be provided to a secondary channel. Theintelligent round robin process will continue to change the primarychannel every three minutes. The secondary channel will likewise bechanged each time the primary channel is changed to distribute powerwithin the laptop cart.

As the laptops are further charged, the amount of power consumed by thelaptops on a given channel will decrease so that power is able to beprovided to all three channels. For example, assume that there are 15amps available, that the primary channel requires 6 amps and that thesecondary channel requires 6 amps. In this instance the control wouldprovide the primary and secondary channels with 6 amps each, and providethe tertiary channel with 3 amps of power. The control would continue toimplement the intelligent round robin cycle to cause the identity of theprimary channel to vary so that each of the channels would be affordedan opportunity to be the primary channel. As power is made availablebecause it is not required by the primary channel, the power is shiftedto the other channels to minimize the overall amount of time required tocharge the laptops.

As the laptops become closer to being fully charged, the amount of powerconsumed by the laptops will continue to decrease until eventually thecontrol is able to provide full power to each of the channels. Thecontrol will do this so that all laptops on each of the channels is ableto be charged.

When the laptops are charged, therefore, the control 210 causes power tobe provided on each of the channels. This allows the laptops to drawoperating current from the channels rather than from the batteries whilestored in the cart. In normal sleep mode, a laptop may draw a very lowamount of power, for example on the order of 0.01 Amps. Thus, leavingthe channels ON does not consume significant energy, but allows thebatteries to remain fully charged while allowing the laptops to pulltheir power requirements from the external power supply. Thus, if thelaptops are stored in the cart for an extended period of time, they willcontinue to be fully charged and the batteries will not be required tobe used to power the laptops during the extended storage period(assuming the cart is plugged in).

Keeping the channels in the powered state also allows the control todetect if an uncharged laptop is connected to any channel. For example,if the channel is populated with 8 fully charged laptops and anuncharged laptop is then connected to the channel, the current sensorwill sense that current is being drawn from the channel. The control cantherefore determine when even one uncharged laptop is connected to agiven channel and, hence, as laptops are plugged into the cart, thecontrol will automatically sense their state of charge and distributepower within the cart to enable the laptops to be charged regardless ofwhere they are plugged into the cart.

The ability to provide full power to one channel and divert theremaining power to one or more of the other channels is provided, in oneembodiment, through the use of relays 213. As shown in FIG. 18, eachchannel has both a TRIAC 216 and a relay 213. The TRIAC is used whileturning the channel on or off, and the relay is used while in steadystate to regulate power onto the channel.

When the control is going to turn on a channel, the control will firstturn on the TRIAC 216, wait a very short period such as 50 ms and thenturn on the relay 213, and then turn off the TRIAC 216. The oppositeprocess is used to turn off the channel. Specifically, if the relay ison, the control 210 will turn on the associated TRIAC 216, turn off therelay 213, and then turn off the TRIAC 216. This allows the TRIAC to beused to absorb the electrical stress and to shield the relay 213.

In one embodiment, Zero-crossing switching is used to enable the AC linecurrent to be switched at a point in the AC cycle where there is theleast amount of electrical stress to the switches (TRIACs & relays).This also reduces “nuisance tripping” of the AC circuit breaker.

FIGS. 18-21 show an example electrical system 200 that may be used inconnection with a computer cart such as the computer cart of FIGS. 1-17.FIG. 18 shows an overview of the electrical system 200 and FIGS. 19-21show particular aspects of the circuit in greater detail. As shown inFIG. 18, the electrical system has an on/off switch 192 that switchesline power (e.g. 220/120 Volt 50/60 Hz power) to the cart. When the userturns the cart on via switch 192, power is provided to each of thechannels under the control of control 210. Power is also provided toswitching power supply 211 which provides low voltage power to control210. As noted above, zero crossing circuitry 214 is connected to theline power to provide the control 210 with information as to thelocation where the voltage on the line is transitioning through zerovolts.

The electrical system has a control 210 that receives input from theuser via mode selection button 195 and uses the input to selectivelyactivate power to one or more of the channels (channels 1-4). In theillustrated embodiment, channels 1-3 correspond to power strips thatwill be used to charge laptops stored within the computer cart, andchannel 4 is an auxiliary power channel which provides power toauxiliary outlets 191 in power module 190 and to the hidden auxiliaryoutlet in the rear compartment of the cart. The auxiliary outlet may bealways on or may be selectively turned off depending on the modeselected by the user.

When the cart is plugged in and the computer cart is turned on viaon/off switch 192, 120/240 volt AC power 212 will selectively be appliedto one or more of the channels under the control of control 210. Thecontrol 210 uses zero crossing circuitry 214 to detect when the voltageis approximately at zero volts to time activation/deactivation of thecircuits to correspond with a neutral voltage condition on line power212. TRIAC switches 216 and relays 213 are used to selectively turnchannels 1-3 on and off upon application of control signals from control210 on lines 218. Each TRIAC/relay combination collectively forms aswitch to turn on/off a particular channel within the laptop cart.

A current sensor 220 is used to sense an amount of current used by aparticular channel. The current sensor 220 enables the control todetermine how much current is being used by a channel so that all theavailable power is utilized within the laptop cart. In one embodiment,the control 210 performs analog to digital conversion to convert theanalog output from the current sensor into a digital signal. Forexample, the controller may sample the signal output from the currentsensor at a particular frequency (e.g. 80 times per cycle) and integratethe current signal from the current sensor 220. This allows the controlto know the amount of current being drawn by the channel. Softwarewithin the control 210 then enables the intelligent round robindistribution of power within the laptop cart as described above.

In one embodiment, the auxiliary channel is always powered to enable theoutlets associated with the auxiliary channel to be available for useregardless of the charging state of the other channels within thecomputer cart. However, the auxiliary outlets may not always requirepower, since it may be that nothing is plugged into any of the auxiliaryoutlets. Hence, in one embodiment, available power not used on theauxiliary circuit is diverted to the other channels to allow all of thepower within the cart to be intelligently utilized. In this embodiment,the current sensor #4 associated with the auxiliary channel #4 is usedto detect how much power is being drawn by devices connected to theauxiliary outlets 191. The balance of the power not used by the devicesconnected to the auxiliary outlets is made available to the otherchannels to thereby increase the amount of power that may be used tocharge the laptops stored within the cart.

In the previous description, an embodiment was described in which thecontrol 210 causes the channel selection to change every three minutes.The invention is not limited to this particular interval, as othersuitably short time interval may be selected instead.

In this embodiment, the control 210 determines a priority of thechannels based on the amount of current used by the channel (as reportedby the current sensors). For example, the control may determine thatchannel #2 requires the most power, channel #1 requires the second most,and that channel #3 requires the least. Initially, the control 210 maythen prioritize the channels #2, #1, #3 and select either one or two ofthe channels to charge, depending on the amount of power available. Theprimary channel #2 may be fully powered, for example, and the secondarychannel #1 may be partially powered. Alternatively, the same amount ofpower may be provided to both channels #2 and #1. After expiration of acharging interval, the control will switch to charge a different set ofchannels. For example, the control may turn channel #2 off and chargechannels #1 and #3. After expiration of a further interval, the controlwill switch to select yet another combination, such as channels #3 and#2. This process will repeat as necessary until the laptops are charged.As the laptops are charged, the laptops will draw less current. Hence,at some point during the charging process, the control will determinethat it has sufficient power to simultaneously activate all laptopcharging channels (#1, #2, and #3). Accordingly, at that point thecontrol will stop using the round robin process and simply activate allof the channels.

FIG. 19 shows an example channel including power strip 50, TRIAC switch216, and current sensor 220. As shown in FIG. 19, TRIAC switch 216receives a control signal from control 210 which activates diode 250.Diode 250 activates low voltage TRIAC 252 to enable gate signal on line254. Voltage at TRIAC 252 is set by resistor R1. Upon application ofgate signal on line 254, TRIAC 256 will cause line power to be appliedto power strip 50. Snubber circuit formed from series connected resistorR3 and capacitor C5 is provided in this embodiment to assist in turningoff TRIAC 256.

Current sensor circuit 220 receives an indication of the amount ofcurrent being drawn by powerstrip 50 on line 260. The signal on line 260is a relatively low voltage. It is passed to amplifier 262 which has again equal to R10/R9. The amplified voltage is passed through a filtercircuit U1B to output current signal ISENSE. The current sense signal isprovided to control 210 where it is integrated to determine the totalamount of current drawn by the channel.

FIG. 20 shows an example zero crossing detection circuit. Other zerocrossing detection circuits may be used as well. Use of zero crossdetection circuitry enables TRIAC 216 to be turned on when the linevoltage is close to zero volts, to prevent switching the outlets on/offat higher voltages.

FIG. 21 shows an example relay switch that may be used in the powersystem shown in FIG. 18. As noted above, the relay switch 213 operatesin parallel with TRIAC switch 216 to regulate the amount of powerprovided to a given channel. The TRIAC protects the relay from transientvoltages while the relay is being turned on/off, and the relay regulatesthe amount of power provided to the channel while active. The use ofrelay switches enables the operator to select, for example, to chargeonly one of the channels manually for a period of time. The control 210provides control signals to both relays 213 and TRIAC switches 216 toprovide the user with control over how the laptops within the cart arecharged.

The functions described herein attributed to the control 210 may beimplemented as a set of program instructions that are stored in acomputer readable memory and executed on one or more processors. Thefunctions attributed to control 210 may also be implemented usingdiscrete components, integrated circuitry such as an ApplicationSpecific Integrated Circuit (ASIC), programmable logic used inconjunction with a programmable logic device such as a FieldProgrammable Gate Array (FPGA) or microprocessor, a state machine, orany other device including any combination thereof. Programmable logiccan be fixed temporarily or permanently in a tangible medium such as aread-only memory chip, a computer memory, a disk, or other storagemedium. All such embodiments are intended to fall within the scope ofthe present invention.

It should be understood that various changes and modifications of theembodiments shown in the drawings and described in the specification maybe made within the spirit and scope of the present invention.Accordingly, it is intended that all matter contained in the abovedescription and shown in the accompanying drawings be interpreted in anillustrative and not in a limiting sense. The invention is limited onlyas defined in the following claims and the equivalents thereto.

1. An electrical system for a computer cart, comprising: a control; anda plurality of electrical channels, each of the plurality of electricalchannels including a switch operatively connected to the control, apower strip having a plurality of electrical outlets to provide power tocomputers stored within the computer cart; and a current sensorconfigured to detect an amount of power being used on the electricalchannel and provide a current sense signal to the control.
 2. Theelectrical system for the computer cart of claim 1, wherein the controlis programmed to determine from the current sense signals the amount ofpower required by each of the plurality of electrical channels to divertelectrical power within the computer cart.
 3. The electrical system forthe computer cart of claim 1, wherein the current sense signal is ananalog signal, and wherein the control digitizes the current sensesignal and integrates the current sense signal to determine a totalamount of current being used by channel.
 4. The electrical system forthe computer cart of claim 1, wherein the control is programmed toimplement an intelligent round robin power distribution process.
 5. Theelectrical system for the computer cart of claim 4, wherein theintelligent round robin power distribution process causes all power tobe distributed to each of the channels in sequence if the channels areable to consume all available power.
 6. The electrical system for thecomputer cart of claim 4, wherein the intelligent round robin powerdistribution process selects a primary channel and provides the primarychannel with full power, and wherein the selection of the primarychannel changes frequently to allow all channels to be fully poweredseveral times within a sixty minute period.
 7. The electrical system forthe computer cart of claim 6, wherein the intelligent round robin powerdistribution process causes a new primary channel to be selectedapproximately every 3 minutes.
 8. The electrical system for the computercart of claim 4, wherein the intelligent round robin power distributionprocess selects both a primary channel and a secondary channel, andwherein the intelligent round robin power distribution process causesthe primary channel to be provided with enough power to fully meetdemand on the primary channel, and wherein any excess power within thepower cart will be provided to the secondary channel.
 9. The electricalsystem for the computer cart of claim 4, wherein the intelligent roundrobin power distribution process selects a primary channel, a secondarychannel, and a tertiary channel, and wherein the intelligent round robinpower distribution process first attempts to meet any power demands ofthe primary channel, then attempts to meet any power demands of thesecondary channel, and then attempts to meet any power demands of thetertiary channel.
 10. The electrical system for the computer cart ofclaim 4, wherein the control is programmed to intelligent round robinpower distribution process causes all channels to become fully poweredas an amount of load on the channels decreases.
 11. The electricalsystem for the computer cart of claim 1, wherein the control isprogrammed to detect when all computers connected to one of the channelsis charged.
 12. The electrical system for the computer cart of claim 11,wherein the control will preferentially divert power away from low loadchannels to higher load channels until all channels are connected tocomputers that are fully charged.
 13. The electrical system for thecomputer cart of claim 12, wherein the control is programmed to providepower to all channels once all channels are connected to computers thatare fully charged.
 14. The electrical system for the computer cart ofclaim 13, wherein the control is able to detect when a single unchargedlaptop is connected to a channel.
 15. The electrical system for thecomputer cart of claim 1, wherein each switch comprises a TRIAC and arelay switch, the TRIAC being designed to protect the relay when therelay switch is turned on or off, and the relay switch being designed toprovide variable power to the channel under the control of the control.16. The electrical system for the computer cart of claim 1, furthercomprising zero crossing circuitry connected between an AC power sourceand the control to enable the control to detect when the AC power sourcehas a voltage of approximately zero volts to enable the control to causethe switch to be activated while the AC power source has a voltage of isapproximately zero volts.